The present invention is directed generally to apparatus for grinding material for use in many different commercial activities where the material has a desired size or fineness grade and, more particularly, an improved drive shaft and method that allows for early detection of drive shaft bearing failure and that provides secondary support for the shaft and associated grinding apparatus in the event of bearing failure.
Various prior designs of grinding apparatus or roller grinding mills are known to the art. In general, the grinding apparatus of prior designs include a frame or housing and motor driven roller grinding assembly within the housing to grind material against a surface, sometimes referred to as a bullring. The grinding assembly, often a plurality of grinding rollers, is supported by a central shaft. The shaft usually has at least one supportive bearing assembly adjacent the bottom of the housing. The central shaft, which functions as a drive shaft, is operatively connected to thrust bearing in a gearbox and the gearbox is operatively associated with an electric motor, often via a clutch. The basic grinding apparatus may be associated with other peripheral apparatus such as separators, dryers and so forth. Examples of the inventor's prior grinding apparatus include U.S. Pat. Nos. 5,839,673; 5,611,494; 5,383,612; 4,830,290; 4,640,204; 4,522,343; 4,478,371; 4,184,640; 4,022,387; and 3,337,142.
In prior art grinding apparatus having drive shafts, failure of the support bearing could result in the shaft and, consequently the grinding assembly, slipping downward resulting in grinding mill failure. In most cases, there is no forewarning of bearing failure, which may result in the operator waiting to replace the bearings until after failure or to prematurely replace the bearings as a preventative measure. In the event the user wants to replace the bearings before complete bearing failure, the gearbox must be removed, the grinding assembly suspended within the housing, and the shaft lowered to allow access to the bearing. In some prior art roller grinding mills, which are not constructed to permit the removal of the shaft and bearing directly out of the bottom of the mill after removal of the gearbox, the entire mill must be disassembled to remove the shaft and bearing.